1 Answer

Most likely you have not captured the real 802.11 frames but are dealing with "fake" Ethernet frames. You can verify this by looking at the Encapsulation type listed in Wireshark's "Statistics -> Capture File Properties" page. If it says, "Ethernet", you don't have 802.11 frames, thus your filter isn't going to work.

Comments

And that screenshot looks Windows-ish; you won't get real 802.11 frames on most platforms, including Windows, unless you're capturing in monitor mode, and, on Windows, you can only capture in monitor mode if you have Npcap, rather than WinPcap, installed. Wireshark's installer installs WinPcap; you would have to install Npcap yourself.